Which image was shot with a filter and which was shot without??? Both with D70 and Nikkor 70-200 VR. See exif info. Shot in NEF and saved to good quality full size JPG using Nikon Browser
A Nikon L37C was used. This is a "UV Filter". Some people recommend the Nikon NC filter because they believe UV filters will color shift the image. I think that's good advice, since there is no need for UV protection for Nikon digital sensors, although I examined these images in Photoshop, looking at individual RGB values and could not detect any shift. Maybe you can find a shifted pixel.
One of the most requently asked questions on photo forums: Should I use a filter?
Here is some sensible advice for the average person asking this question.
1. If you think one of these images is noticably degraded, then don't use a filter.
2. If you can't tell the difference and you need to ask this question, buy a filter and use it.
3. When shooting into the light, for sunsets and sillouettes, for example, take it off. You WILL get reflections with most filters and lenses. When you do take it off, your lens will be pristine. A dirty lens will also degrade into the light images. You won't have to do those "emergency cleanings" in the field (usually with your shirt, from what I see) that do the real damage to lens coatings and surfaces.
4. People who recommend against using filters will not come to your house and clean your lens, nor will they replace it for you if you damage it. Interestingly, they never post images showing degredation of normal front-lit images.
5. If you don't know the answer to this question (for your own personal use), you probably don't know how to clean a filter and even if you have read something somewhere, you probably don't have much if any experience with this.
6. Convinced? Buy a filter. Use it. Take it off when shooting into the light. Clean it when it needs cleaning. In a year or two, look at the outer surface of your filter. If you are satisfied with the condition of the filter, and you think it degrades your images, take it off and leave it off. I'll bet, though, that you will be unhappy with the condition of your filter, which, at best, will have an accumulation of residue that no amount of cleaning will quite remove. It may have spots where liquids have damaged the coatings and it may have some sleeks from sand or dust motes wiped off the surface.
Cleaning optical glass is a Black Art. Many makers and knowledgable sellers of expensive astronomical telescopes actually recommend never cleaning the surface, except when it absolutely needs it. Most photographers constantly clean their lenses and filters.
The real damage is done by rubbing sand and other tiny hard particles across the glass, even when using a clean microfiber cloth. The coatings on good lenses and filters are only a few molecules thick. These hard particles can easily remove a bit of the coating and if you are careless can leave a haze over time. Same, of course, if using a rough or dirty cloth such as your shirt, which seems to be the favorite lens cleaning cloth while in the field (I've seen it dozens of times).
Use an air blower first, to try to dislodge as many hard particles as posssible, before wiping the lens. Some of the particles will stick to the lens; that is where the Black Art comes in. Good luck!
7/8/2008 Update: I added a new pair of test images (115944-5), now with the higher rez D200 and what at least Bjorn Rorslett apparently considers one of the sharpest lenses made, the 35/1.4 Ai.
This time I stacked not one, not two, but THREE Nikon L37C filters on top of each other (see photo) and used a nicer scene with lots of varied detail. The RAW images were opened in Nikon Capture NX 1.2, in camera sharpening setting removed and replaced with USM 55-5-4, which I find more satisfactory with this lens. This is one incredibly sharp lens! Both images shot with a Nikon HN-23 hood.
I defy you find a difference between these images at less than 600% zoom :-)
Oh yea, the 3 filters were picked at random from 6 or so sitting on various lenses. They all have at least a year of accumulated residue on them, which I did not bother to clean, just to illustrate another point. I did blow the dust off with a rocket bulb. The filters look like they need a cleaning, but then, do they really? You be the judge.
1/3/2011 Update: In reviewing DSCN_115944 and DSCN_115945 I see that it was originally shot with "Auto" tone compensation. I re-rendered the images today using "Normal" tone compensation to ensure that there was no variance in the D200's computation of it's Auto tone compensation. I did not see a meaningful difference but others might depending on their definition of meaningful. These new images were rendered from NEF files using Capture NX2 V2.2.4 with Daylight white balance, Capture NX USM of 55/5/4 with in camera sharpening turned off, Normal saturation and color mode Mode III.